Resin delivery system with air flow regulator

ABSTRACT

Apparatus and methods for conveying granular plastic resin from a supply to receivers that retain and dispense the resin when needed by process machine include a vacuum pump, an air flow limiter connected to the suction head of the vacuum pump, a first conduit connecting the receivers to the air flow limiter, and a second conduit connecting the resin supply to the receivers.

CROSS-REFERENCE TO RELATED PATENT APPLICATION

This patent application is a 35 USC 120 continuation-in-part of U.S.Ser. No. 14/185,016 entitled “Air Flow Regulator” filed 20 Feb. 2014 inthe name of Stephen B. Maguire, the priority of which is claimed under35 USC 120. The disclosure of the '016 application is herebyincorporated in its entirety by reference.

BACKGROUND OF THE INVENTION

This invention relates to manufacture of plastic articles and moreparticularly relates to pneumatic conveyance and processing of plasticresin pellets prior to molding or extrusion of those pellets into afinished or semi-finished plastic product.

In this patent application, injection and compression molding pressesand extruders are collectively referred to as “process machines.”

BACKGROUND OF THE INVENTION—DESCRIPTION OF THE PRIOR ART

Current resin central loading systems concerned with conveying granularplastic resin pellets from a storage area for molding or extrusiontypically include a vacuum pump or pumps and multiple receivers.

In some systems, with many receivers, several small pumps are used.

It would be less expensive to use only one, or fewer, larger pumps.However, a larger pump may draw too much air with resulting damage tothe material being conveyed. While a larger pump could load severalreceivers at once, there is a risk that an “open” line, namely a linepulling only air, and no resin material, would cause the vacuum to droptoo much, and no resin would load. Also, when only one receiver isloading resin, air velocity might be too high, again with a risk ofdamaging the resin.

Nevertheless, in facilities that fabricate plastic products by moldingor extrusion, it is common to use such vacuum loading systems topneumatically convey pellets of thermoplastic resin, prior to molding orextrusion of those pellets into a finished or semi-finished product. Theplastic resin pellets are typically purchased in 50 pound bags, 200pound drums, or 1,000 pound containers commonly referred to as“Gaylords.”

A preferred approach for conveying plastic resin pellets from a storagelocation to a process machine, which approach is often used in largerfacilities, is to install a central vacuum pump or even several vacuumpumps, connected by common vacuum lines to multiple “receivers.”

Vacuum pumps connected to the vacuum lines draw vacuum, namely air atpressure slightly below atmospheric, as the vacuum pump sucks airthrough the “vacuum” line. The suction moves large quantities of airwhich carries thermoplastic resin pellets through the “vacuum” line.

An alternative is to use positive pressure produced by a blower or theexhaust side of a vacuum pump. With such an approach, the positivepressure results in a movement of substantial amounts of air which maybe used to carry the plastic resin pellets. However, the vacuum approachof drawing or sucking pellets through the system conduits is preferableto the positive pressure approach of pushing the resin pellets throughthe system conduits.

In practice, vacuum pumps are preferred and vacuum lines are desirablein part because power requirements to create the required vacuumnecessary to draw plastic resin pellets through the lines are lower thanthe power requirements if the plastic resin pellets are pushed throughthe lines by a blower or by the exhaust side of a vacuum pump. Whenvacuum is used, the static pressure within the line may be not much lessthan atmospheric. When positive pressure is used, the dynamic pressureof the air flowing through the line must be relatively high in order tomove an adequate quantity of plastic resin pellets.

As used herein, and in light of the foregoing explanation, the terms“vacuum pump” and “blower” are used interchangeably.

When one or more central vacuum pumps are connected to multiplereceivers, a receiver is typically located over each temporary storagehopper, in which the plastic resin pellets are temporarily stored beforebeing molded or extruded. A temporary storage hopper is typicallyassociated with each process machine.

In current practice, the receiver is connected by a control wire to acentral control system. The control system works by selectively openinga vacuum valve located in each receiver, allowing one or several vacuumpumps to work in sequence drawing “vacuum”, i.e. below atmosphericpressure air, to carry the pellets among and to multiple receivers asindividual ones of the receivers, positioned over individual hoppersassociated with the individual process machines, require additionalplastic resin pellets. The receiver for a given hopper-process machinecombination is actuated by opening the vacuum valve located in or nearthe receiver, causing the receiver to supply plastic resin pellets bygravity feed into the hopper from where the pellets may be fed furtherby gravity downwardly into the associated process machine.

Large, high capacity industrial vacuum pumps are reliable and are suitedto heavy duty industrial use. Large high capacity vacuum pumps allowlong conveying distances for the plastic resin pellets. Currentlyavailable large capacity vacuum pumps permit plastic resin pellets to beconveyed over distances of 200 feet or more using vacuum drawn by thepump. Use of such high capacity vacuum pumps results in a big rush ofbelow atmospheric pressure air through the line, carrying the plasticresin pellets over a long distance.

Operators of plastic manufacturing facilities prefer to buy plasticresin pellets in bulk, in rail cars or tanker trucks. Bulk purchasesresult in cost savings. Plastic resin pellets delivered in bulk aretypically pumped into large silos for storage. In a large manufacturingfacility, the distance from a plastic resin pellet storage silo to aprocess machine may be several hundred feet, or more. Accordingly, whenplastic resin pellets are purchased in bulk, a central vacuum-poweredconveying system, powered by one or more large, high capacity industrialvacuum pumps, is a necessity.

Typically, large central plastic resin pellet conveying systems have oneor more vacuum pumps, each typically from 5 to 20 horsepower. Thesecentral systems include central controls connected by wire to eachreceiver associated with each process machine in the facility. Typicallyeight, sixteen, thirty-two or sixty-four receivers, each associated witha process machine, may be connected to and served by the central plasticresin pellet vacuum conveying system. Of course, the higher the numberof receivers served by the system, the higher the cost.

A factor to be considered in designing such a system is the speed of theplastic resin pellets as they flow through a conduit as the plasticresin pellets are carried by the moving air stream drawn by the vacuumpump. If air flow is too slow, the plastic resin pellets fall out of theair stream and lie on the bottom of the conduit, with resulting risk ofclogging the conduit. If air flow is too fast, the plastic resin pelletscan skid along the conduit surface. In such case, harder, more brittleplastic resin pellets may be damaged, resulting in dust within theconduit, which when drawn into the vacuum pump can damage the vacuumpump and render the system inoperative. Softer plastic resin pelletsheat up and can melt from friction when contacting the conduit interiorsurface. This results in “angel hair”—long, wispy-thin strands ofplastic film which eventually clog the conduit and cause the system toshut down.

For these reasons, pneumatic plastic resin pellet conveying systems mustbe designed to produce desired, reasonable conveying speeds for theplastic resin pellets.

Currently, conveying speed of the plastic resin pellets is most oftencontrolled by controlling air flow, measured in cubic feet per minute,and varying the desired and designed cubic feet per minute based onconduit diameter, with a larger diameter conduit requiring more cubicfeet per minute of air flow to maintain proper air flow speed throughthe conduit. Controlling air flow, measured in cubic feet per minute, isconventionally done by properly specifying the vacuum pump by capacityand, in some cases, by varying speed of the vacuum pump as the vacuumpump draws the air in a “vacuum” condition through the conduit, carryingplastic resin pellets in the moving, below atmospheric pressure air.Controlling cubic feet per minute of air flow is an indirect way ofcontrolling plastic resin pellet speed as the plastic resin pellets flowthrough a conduit of a given diameter.

Typically, a 2 inch diameter conduit requires about 60 cubic feet perminute of air flow to convey typical plastic resin pellets. A 2½ inchdiameter conduit typically requires about 100 cubic feet per minute ofair flow to convey typical plastic resin pellets. To achieve thesedesired air flow volume flow rates, a conventional designer mustcarefully match the horsepower of a vacuum pump, which has a given cubicfeet of air per minute rating, to a selected size conduit, taking intoconsideration the average distance the plastic resin pellets must beconveyed through the conduit from a storage silo to a receiver orloader. If this results in selection of a 5 horsepower blower/vacuumpump, then a given facility may require several such blowers/vacuumpumps, with each blower/vacuum pump supplying only a selected number ofreceivers.

A single plastic resin molding or extruding facility might theoreticallyrequire a 20 horsepower blower and the corresponding cubic feet perminute capability for the conveyance provided by the single blower tomeet the total conveying requirements for plastic resin pelletsthroughout the facility. However, a single twenty horsepower blowerwould result in far too high a conveying speed for the plastic resinpellets through any reasonable size conduit. As a result, the conveyingsystem for the plastic resin pellets in a large facility is necessarilydivided and powered by three or four smaller blowers, resulting in threeor four different, separate systems for conveyance of plastic resinpellets. Sometimes several blowers are connected to a single set ofreceivers, with one or more of the extra blowers turning “on” only whenrequired to furnish the required extra cubic feet per minute of airflow. This is controlled by a central station monitoring all receiversand all blowers, with the central station being programmed to maintainall of the hoppers associated with the process machines in a fullcondition, wherever those hoppers are located throughout the facility.

Even with careful planning and design, results achieved by suchpneumatic plastic resin pellet conveying systems are not consistent. Airflow speed and cubic feet per minute capacity of blowers often vary andare outside of selected design and specification values.

SUMMARY OF THE INVENTION

The instant invention provides an improvement to known pneumatic plasticresin pellet conveying systems, reducing the costs of those systemswhile providing consistent control of delivered cubic feet per minute ofair for individual receivers. The invention also facilitates easyexpansion of the pneumatic plastic resin pellet conveying system as thesystem grows. Such expandable systems are made feasible by an inventiveair flow controller embodying aspects of this invention. The air flowcontroller is a new cubic feet per minute air flow regulator.

In one aspect of this invention, air flow control devices, desirably ofthe type disclosed in co-pending U.S. patent application Ser. No.14/185,016 entitled “Air Flow Regulator”, filed 20 Feb. 2014 in the nameof Stephen B. Maguire, are added to each receiver so that the air pulledfrom any single receiver is limited to the correct predetermined,preselected flow rate. This prevents excessive flow rates and “open”lines that dump too much air into the system.

Use of these air flow regulators allow one large pump to be used withoutrisk to the system or to the resin being conveyed. An added advantage ofa very large pump is that it can fill multiple receivers simultaneouslywith resin. As used herein, the term “receiver” denotes the type ofapparatus disclosed in U.S. Pat. Nos. 6,089,794; 7,066,689, and8,753,432. The disclosures of these patents are hereby incorporated byreference.

The invention allows receivers to “load” the resin the instant there isdemand for material by dropping the material downwardly into agravimetric blender or directly into a process machine. The receiverneed not wait in the “queue” to load because no sequencing of thereceivers is required. Each receiver is always “ready to go.”

A central control station is not required, and neither is wiring fromeach receiver to a central control station, thus further reducing costs.

Consequently, in this invention as implemented in one of itsembodiments, there are one or several large vacuum pumps, with receiversthat stand alone without need for a central control, and an air flowlimiter on each receiver to assure proper and constant flow rate.

This invention facilitates reducing the speed of the vacuum pump, tohold the desired vacuum level in the lines. This is in contrast torunning the vacuum pump at full speed all the time.

“CFM” is a term referring to a cubic foot of air regardless of thedensity of the air. “SCFM” refers to a cubic foot of air at standardtemperature and pressure, namely 70° F. at sea level. The air flowlimiter of the instant invention holds SCFM constant. This means thatair flow through the air flow limiter aspect of the invention will befaster when the air is thin, such as at high altitudes, and slower whenthe air is thick, such as at sea-level. However, in both cases (or anycase), the air flow limiter maintains SCFM, namely air flow in standardcubic feet per minute, constant. Stated differently, so long as the SCFMis held steady, as is the case with the air flow limiter of the instantinvention, the same weight of air, or number of air molecules, flowsthrough the limiter regardless of conditions. It is just that air flowrate through the limiter may change in terms of the speed of the air,but in all cases, the quantity of air flowing, measured in standardcubic feet per minute, is constant.

In another embodiment of the invention one air flow limiter, asdisclosed in the instant application, is in place as a single air flowlimiter at the vacuum pump suction inlet with the vacuum pump beingconnected to a plurality of receivers all connected in a system. Thisprovides a selected, correct rate of air flow in standard cubic feet perminute. In this embodiment of the invention, only a single air flowlimiter is used at the vacuum pump inlet, as opposed to the alternativeembodiment of the invention described above where one air flow limiteris used at each receiver.

An advantage of using only a single air flow limiter of the typedisclosed herein is that the vacuum pump can be sized and operated forthe longest distance over which resin is to be conveyed in a givenlocale. This can be done while still protecting shorter runs of thesystem from excessive resin material velocity, where less vacuum isrequired. One air flow limiter costs less than having an air flowlimiter located at every receiver; this provides an advantageous aspectto this embodiment of the invention.

By adding an air flow limiter manifesting aspects of this invention toevery receiver, plant operators can control air flow in cubic feet perminute to a maintained, constant value that is ideal for that particularreceiver, considering conduit diameter and distance over which theplastic resin pellets must be conveyed through that conduit.Alternatively, by adding an air flow limiter manifesting aspects of thisinvention just to the suction inlet of the vacuum pump, a plant operatorcan control air flow in cubic feet per minute to a constant value thatis ideal for the system as a whole, considering conduit diameter anddistance over which the plastic resin pellets must be conveyed to themultiple receivers in the system.

Use of the air flow limiter in accordance with this invention allowspneumatic plastic resin pellet conveying systems to utilize a singlelarge high horsepower vacuum pump. In accordance with one embodiment ofthe invention, each receiver in a facility is fitted with an air flowlimiter embodying the invention so the flow for each receiver in cubicfeet per minute is self-limiting. This approach eliminates the need tomatch vacuum pumps or blowers to a specific material conduit size orconveyance distance. Using this approach, the flow limiter of theinvention permits operators to run a very large vacuum pump or blower ata speed that will maintain a desired high level of vacuum throughout theentire vacuum (or pneumatic) plastic resin pellet conveying system.

Using larger than standard diameter vacuum conduits allows a significantvacuum reserve to exist in the plastic resin pellet conveying system,without the need for a vacuum reserve tank. Larger diameter conduitsalso mean there is little loss of vacuum over long distances, even atthe most distant receiver to which plastic resin pellets are supplied bythe system. A variable frequency drive control may be used to adjust thespeed of the vacuum pump to maintain air flow at the desired standardcubic feet per minute rate through the air flow limiter.

With the flow regulator aspect of the invention facilitating use of highhorsepower vacuum pumps or blowers, designers utilizing the inventioncan now design to load multiple receivers at the same time without fearof dropping vacuum levels too low in portions of the pneumatic or vacuumplastic resin pellet conveying system.

In the plastic resin pellet conveying system aspect of the invention, nocentral control system is required. Using the flow limiter of theinvention, each receiver controls its own operation and is not wired toany central control facility. When the level of plastic resin pellets inthe hopper of a process machine falls to a sufficiently low level, alevel sensor tells the receiver to load the hopper of the processmachine. Coupled to the level sensor may be a vacuum sensor, whichconfirms that the main system has sufficient vacuum available to loadthe receiver. If too many other receivers are currently loading, and thevacuum level is sensed to be below the threshold for effective loading,then the receiver associated with the sensor will wait until vacuumreadings rise. When available system vacuum is sufficient to assureadequate flow of plastic resin pellets into a given receiver, the vacuumsensor causes a vacuum valve associated with the receiver to open theconnection of the receiver to the conduit carrying the plastic resinpellets, and the receiver fills with resin pellets.

In accordance with one aspect of the invention, each receiver acts onits own sensed information. Use of the high horsepower vacuum pump meansthat several receivers can load simultaneously.

The air flow limiter aspect of the invention does several things to makesuch systems in accordance with the invention possible. By limitingcubic feet per minute of flow to the desired constant level, there isvirtually no limit on the horsepower of the vacuum pump. The risk of atoo high a conveyance speed of the plastic resin pellets through theconduit is eliminated. Additionally, if a receiver is not drawing inplastic resin pellets but is just drawing air as a result of the mainsupply of plastic resin pellets being exhausted, the empty conduit ofthe conveying system would ordinarily convey a substantial amount ofair, which normally would drop the vacuum reserve of the entirepneumatic conveying system very rapidly. But with the flow limiter ofthe invention such dumping of air into the conveying conduit is at leastsubstantially reduced, and if the flow limiter is at the suction intakeof the vacuum pump, such dumping of air into the system is essentiallyimpossible.

Further contributing to minimized air dump into the vacuum conduit isthe receiver's ability to detect system failure or absence of materialbeing loaded, thereby stopping further load cycles and sounding analarm.

In the air flow limiter aspect of the invention, the limiter has asingle moving part, a valve, which relies on two opposing forces, namelygravity in one direction and “lift” created by air flow in the oppositedirection. Because the air flow limiter uses gravity to close the valveportion of the regulator, orientation of the air flow limiter isimportant. Air flow must be upward, essentially vertically through theair flow limiter, to counter the downward force of gravity.

The air flow limiter is desirably in the form of a tube with an air flowactuated valve within the tube. In a “no flow” condition, gravity holdsthe valve closed. However, as air flow through the limiter reaches apre-selected design value, air flowing over and against a sail-likeplate lifts an internal free floating valve. This shuts off air flowthrough the air flow limiter if the free floating valve risessufficiently to contact a stop located within the tube.

By adjusting the size and/or shape of the “sail”, and the weight of thefree floating valve, desired air flow in standard feet per minute can beregulated very closely. Gravity as a force in one direction means theopening force is constant over the full range of motion of the valvedevice. (A spring, if one were used, would provide a variable force.However, use of gravity in the air flow limiter aspect of the inventioneliminates that variable).

In the air flow limiter aspect of the invention, at the desired designstandard cubic feet per minute of air flow, the valve opens as air liftsit. The valve would continue moving upwardly except for the fact thatthe valve reaches a point of air flow restriction, where the valve holdsair flow steady at the desired design value. If the valve moves furtherupwardly towards a “closed” position, this reduces air flow andresulting force in the valve, causing the valve to drop in response togravity. If the valve drops below the control level, this allows moreair flow and consequently the valve rises as the air pushes the valveupwardly. As a result, the valve reaches the desired design valveequilibrium control point essentially instantly and very accurately.

Known air flow shutoffs are subject to “vacuum pull”, causing them toshut off completely once air begins to flow. This is because in knownshutoffs, vacuum “pull” of the vacuum pump is always present. In the airflow limiter of the invention, a short vertical tube closes against aflat horizontal surface. In the air flow limiter of the invention, airflow is directed through the center of the short tube and escapes overthe top edge of the short tube and then around open edges of a flatshutoff surface. A flat, desirably triangular or star-shaped plate ispositioned in the air flow below and connected to the short tube. Thisplate acts as a sail in the air flow and will, at the designed desiredstandard cubic feet per minute air flow rate, provide enough lift toraise the short tube against the shutoff plate.

At shut off, with vacuum above the flat shutoff surface and air at somepressure below the flat shutoff surface, most of the air pressure forcesare against the walls of the short tube. Those forces are radiallyoutwardly directed. Specifically, they are horizontal due to theconfiguration of the air flow limiter, and do not exert vertical forcethat would make the movable portion of the valve, namely the short tube,move in a vertical direction.

The surface of the end of the short tube, at the short tube end edge, isa horizontal surface and can provide a small vertical force when airtravelling upwards impinges on the surface. For this reason, the airflow limiter aspect of the invention uses a very thin wall short tube,to minimize this horizontal surface area of the short tube.

In the air flow limiter aspect of the invention, air flow rate in cubicfeet per minute can be adjusted by adding or subtracting weight from thefloating valve, or by adjusting the surface area of the sail, or byadjusting the size or shape of the sail in the air flow.

Accordingly, in one of its aspects, the invention provides a resindelivery system and method that includes an air flow limiter having avertically oriented tube, a pair of open-ended telescoping tubularinternal segments within the tube, with an outer tubular segment beingfixed and the other being slidably moveable along the fixed segment inthe axial direction. The air flow limiter further includes a plateextending partially across the interior of the vertically oriented tubeand positioned for contacting the moveable one of the telescopingtubular segments and limiting travel of the moveable telescoping tubularsegment, with the plate covering the upper, open end of the moveabletelescoping tubular segment upon contact therewith. In this aspect, theinvention yet further includes a sail positioned in the verticallyoriented tube below the telescoping segments, a strut connecting thesail and the moveable telescoping tubular segment, and a bafflepositioned to direct upward air flow within the tube through thetelescoping tubular segments. The moveable telescoping tubular segmentmoves vertically within the tube, unitarily with the sail, responsivelyto air flow upwardly through the tube against the sail.

The tubular segments are preferably cylindrical; the surface of theplate contacted by the moveable tubular segment is preferably planar;and the portion of the moveable tubular segment contacting the platesurface is preferably annular.

In a variation of terminology, a surface of the plate contacted by themoveable tubular segment is flat, the tubular segments are cylindricaland the circular edge of the tubular segment contacting the plateservice is annular and normal to the axis of the tubular segment.

In yet another one of its aspects, this invention provides a resindelivery system having at least one air flow limiter consisting of avertically oriented tube, a tubular segment within the tube, whichsegment is moveable in the axial direction, a plate extending at leastpartially across the interior of the tube for contacting the movabletubular segment and defining a limit of travel of the moveable tubularsegment, a sail positioned in the tube below the moveable tubularsegment and being moveable vertically within the tube, a strutconnecting the tubular segment and the sail, and a baffle connected toand located within the tube defining a lower limit of travel of themoveable tubular segment upon contact of the strut with an upperextremity of the baffle. The moveable tubular segment is in slidingtelescoping engagement with the tubular portion of the baffle, directingupward air flow within the tube, with the moveable tubular segment beingmoveable unitarily with the sail in response to upward air flow throughthe tube contacting the sail.

In yet another one of its aspects, this invention provides a resindelivery system that includes at least one air flow regulator having avertically oriented tube with a sail assembly positioned in the tube andmoveable therewithin responsively to air flow through the tube toregulate air flow through the tube and to stop air flow thorough thetube upon air flow exceeding a preselected value expressed in standardcubic feet per minute.

In yet another one of its aspects, this invention provides a method forconveying granular plastic resin by controlled air flow where air flowcontrol involves the steps of providing a vertically oriented tube,positioning a moveable sail assembly including a sail within the tube,positioning a stop within the tube, and permitting the sail assembly tomove responsively to air flow through the tube between a position atwhich air flows around the sail assembly and through the tube, and aposition at which the sail assembly contacts the stop and blocks airflow through the tube.

In yet another one of its aspects, this invention provides a pneumaticresin delivery system utilizing air flow regulating apparatus includinga vertically oriented first tube, a vertically oriented second tubewhich is moveable along and within the first tube, a baffle within thefirst tube for forcing air flow in the first tube through the secondtube, a guide within the first tube for limiting the second tube tovertical co-axial movement within and relative to the first tube, a sailwithin the first tube being connected to the second tube and beingmoveable responsively to air flow within the first tube, and a stopwithin and connected to the first tube for limiting vertically upwardtravel of the second tube.

In still another one of its aspects, this invention provides apparatusfor conveying granular plastic resin from a supply to receivers thatretain and dispense the resin when needed by a process machine, wherethe apparatus includes a vacuum pump, a single air flow limiterconnected to a suction head of the vacuum pump, a first conduitconnecting the receivers to the air flow limiter, and a second conduitconnecting the granular material supply to the receivers. In thisembodiment of apparatus of the invention, suction created by operationof the vacuum pump draws granular plastic resin from the supply into thereceivers through the second conduit and draws air from the secondconduit through the receivers, the first conduit and the air flowlimiter. The air flow limiter is oriented in a vertical direction forvertical flow of air upwardly therethrough.

In yet still another aspect, this invention provides apparatus forconveying granular plastic resin material from a supply of resinmaterial to receivers that retain and dispense the resin material whenneeded by a process machine, where the apparatus includes a vacuum pump,air flow limiters connected to outlets of the receivers, with the airflow limiters being vertically oriented for vertical flow of air drawnby suction therethrough, a first conduit connecting the air flowlimiters to a suction head of the vacuum pump and a second conduitconnecting the granular resin material supply to the receivers. In thisapparatus aspect of the invention, suction created by operation of thevacuum pump draws granular plastic resin from the supply of granularplastic resin material into the receivers through the second conduit,and also draws air from the second conduit through the receivers, theair limiters, and the first conduit. In this second embodiment, at leastone of the air flow limiters preferably consists of a tube, a tubularsegment within the tube that is moveable in the axial verticaldirection, a plate extending at least partially across the interior ofthe tube for contacting the moveable tubular segment and defining alimit of vertical travel of the moveable tubular segment, a sailconnected to the moveable tubular segment and being moveable therewithwithin the tube, and a baffle connected to and within the tube defininga second limit of vertical travel of the moveable tubular segment, wherethe moveable tubular segment is in sliding telescoping engagement withthe tubular portion of the baffle and the baffle directs air flow withinthe tube into the tubular segment. The moveable tubular segment movesunitarily with the sail in response to vertical air flow through thetube contacting the sail.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic representation of a resin delivery system with asingle air flow regulator in accordance with aspects of the invention.

FIG. 2 is a schematic representation of a resin delivery system with aplurality of air flow regulators in accordance with aspects of thisinvention.

FIG. 3 is an isometric view of the exterior of an air flow limiterportion of apparatus for pneumatically conveying granular plastic resinthat aspects of the invention.

FIG. 4 is a front elevation of the air flow limiter illustrated in FIG.3.

FIG. 5 is an isometric sectional view of the air flow limiterillustrated in FIGS. 3 and 4, with the section taken at arrows 3-3 inFIG. 4.

FIG. 6 is a sectional view in elevation of the air flow limiterillustrated in FIGS. 3 and 5, with the section taken at lines and arrows3-3 in FIG. 4, with air flow through the air flow limiter being depictedin FIG. 6 by curved dark arrows.

FIG. 7 is a sectional view in elevation similar to FIG. 6 but with theair flow limiter internal parts in position whereby there is no airentering the air flow limiter and hence there is no air flow upwardlythrough the air flow limiter, in contrast to such air flow being shownin FIG. 6.

FIG. 8 is a sectional view in elevation similar to FIGS. 6 and 7 butwith the air flow limiter internal parts in position where there is anexcessive amount of air attempting to enter the air flow limited butthere is no air flow upwardly through the air flow limiter due to theair flow limiter valve having moved to block air flow upwardly throughthe air flow limiter, in contrast to air flow upwardly through the airflow limiter as shown in FIG. 4.

FIG. 9 is an exploded isometric view of the air flow limiter illustratedin FIGS. 3 through 8.

FIG. 10 is an isometric view of the movable portion of the air flowlimiter illustrated in FIGS. 3 through 9.

FIG. 11 is a sectional view of the air flow limiter similar to FIGS. 6,7 and 8, illustrating an alternate construction of the baffle portion ofthe air flow limiter.

FIG. 12 is sectional view of the air flow limiter similar to FIGS. 6, 7,and 11, illustrating a second alternate construction of the baffleportion of the air flow limiter.

DESCRIPTION OF THE PREFERRED EMBODIMENT AND BEST MODE KNOWN FOR PRACTICEOF THE INVENTION

In this application, unless otherwise apparent from the context it is tobe understood that the use of the term “vacuum” means “air at slightlybelow atmospheric pressure.” The vacuum (meaning air slightly belowatmospheric pressure) provides a suction effect that is used to drawgranular plastic resin material out of a supply and to convey thatgranular plastic resin material through various conduits to receiverswhere the granular resin material can be temporarily stored before beingmolded or extruded. Hence, in this application it is useful for thereader mentally to equate the term “vacuum” with the term “suction”.

Referring to the drawings in general and to FIG. 1 in particular,apparatus for conveying granular plastic resin material from the supplyto receivers that retain and dispense the resin material when needed bya process machine is illustrated in FIG. 1. The apparatus, which isdesignated generally 88 in FIG. 1, preferably includes a vacuum pumpdesignated generally 92 and shown schematically in FIG. 1. The vacuumpump preferably includes a vacuum pump suction head 93 also shownschematically in FIG. 1. Connected to the vacuum pump suction head 93 isan airflow limiter 30 shown only in schematic form in FIG. 1, but shownin detail in FIGS. 3 through 12. Airflow limiter 30 receives vacuumdrawn by vacuum pump 92 through vacuum drawing conduit 100.

Vacuum drawing conduit 100 is connected to a plurality of receivers 16,each of which receives, retains and dispenses, as needed, granularplastic resin material to a process machine, such as as a granulatorblender, or an extruder, or a molding press as located preferably belowa receiver 16. The process machines are not illustrated in FIG. 1 toenhance the clarity of the drawing.

Further illustrated in FIG. 1 is a hopper 18 for storage of granularplastic resin material therein and a resin conveying conduit 98, whichserves to draw resin from hopper 18 and to deliver the resin throughresin conveying conduit 98 to the respective receivers as vacuum isdrawn by the vacuum pump, with vacuum propagating through air flowlimiter 30, vacuum drawing conduit 100, the various receivers 16, andresin conveying conduit 98, back to hopper 18.

FIG. 2 shows an alternate embodiment of the resin conveying system ofthe invention where this alternate embodiment of the conveying systemhas been designated 88A. FIG. 2, as in FIG. 1, depicts a vacuum pump 92shown in schematic form having a vacuum pump suction head 93 alsodepicted in schematic form. In the alternate embodiment of the inventionillustrated in FIG. 2, vacuum drawing conduit 100 leads directly intoand communicates with vacuum pump suction head 93. In the embodimentillustrated in FIG. 2, an air flow limiter 30 is provided for eachreceiver 16, with the air flow limiter 30 for a respective receiver 16being located in a portion of a connection conduit 102 that connects arespective receiver to vacuum drawing conduit 100. In FIG. 2, each airflow limiter 30 is depicted in a vertical orientation, just as isairflow limiter 30 depicted in a vertical orientation in FIG. 1. Eachreceiver is connected by connection conduit 102 to vacuum drawingconduit 100 with air flow limiter 30 forming a portion of connectionconduit 102.

In FIG. 2, as in FIG. 1, a first conduit 98 serves to convey granularplastic resin from hopper 18 to the respective receivers in response tovacuum drawn by vacuum pump 92 as that vacuum propagates from vacuumpump 92 through second conduit 100, connection conduits 102, receivers16, and resin conveying conduit 98 to hopper 18.

During operation of the resin conveying systems shown schematically inFIGS. 1 and 2, upon actuation of vacuum pump 92, a vacuum is drawn atvacuum pump suction head 93. This vacuum, as it propagates back tohopper 18, serves to draw resin out of hopper 18 and into the respectivereceivers 16. In the embodiment illustrated in FIG. 2, individual airflow limiters 30 limit the suction or vacuum drawn by vacuum pump 92through a given associated receiver 16. In the embodiment illustrated inFIG. 1, a single air flow limiter 30 limits the vacuum drawn through allof receivers 16 forming a portion of the granular resin conveying systemillustrated in FIG. 1.

Referring to FIGS. 1 and 2, the air flow limiter 30 portion of the resindelivery systems is preferably in the general form of a verticallyoriented tube, preferably having inlet and outlet ends 54, 56respectively. The tubular character of air flow limiter 30 is apparentfrom FIGS. 3 through 8, where air flow limiter 30 preferably includes avertically oriented exterior tube 32, with open-end caps 58, 60 definingand providing open inlet and outlet ends 54, 56 respectively. End caps58, 60 are open, of generally cylindrical configuration, and areconfigured to fit closely about vertically oriented tube 32 so as toprovide a substantially air tight fit between end caps 54, 56 and tube32.

As illustrated in FIG. 5, air flow limiter 30 preferably includes,within vertically oriented exterior tube 32, a horizontally positionedplate 46, which is oriented perpendicularly to the axis of tube 32.Plate 46 is preferably configured as a circular disk of lesser diameterthan the inner diameter of vertically oriented tube 32, with plate 46further preferably including three legs extending outwardly from thecircular interior disk portion of plate 46. Legs of plate 46 aredesignated 62 in FIG. 9, while the circular interior portion of plate 46is designated 64 in FIG. 9. Plate 46 is secured to the interior ofvertically oriented outer tube 32 by attachment of legs 62 to theinterior surface of tube 32. Any suitable means of attachment, such asby welding, adhesive, mechanical screws, or end portion of legs 62defining tabs fitting into slots within tube 32 as shown in FIG. 5, maybe used.

As best shown in FIGS. 5, 6, and 7, a baffle 52 is positioned withinvertically oriented outer tube 32, below plate 46. Baffle 52 has a lowerconical portion 66 and an upper cylindrical portion 44, with cylindricalportion 44 defining a fixed internal tubular segment of air flow limiter30. Baffle 52 is preferably retained in position by a pair of screwsdesignated 68, 70 respectively. Baffle 52 preferably rests on screw 68.Screw 70 preferably fits against the fixed internal tubular segment 44portion of baffle 52 to secure baffle 52 in position within verticallyoriented external tube 32. Lateral force applied by screw 70 in adirection perpendicular to the axis of vertically oriented external tube32, with screw 70 in contact with fixed internal tubular segment 44,serves to effectively retain baffle 52 against movement withinvertically oriented external tube 32.

The upper portion of baffle 52, defining fixed internal tubular segment44, is adapted for sliding telescopic engagement with and movementtherealong by movable tubular segment 42. Fixed to movable tubularsegment 42 is a first strut 48 preferably extending transversally acrossthe upper portion of movable tubular segment 42 and preferably securedon either end to movable tubular segment 42, as illustrated in FIG. 10.Preferably extending downwardly from first strut 48 is a second strut50, preferably secured to first strut 48 and preferably also to a sail34, as illustrated in FIG. 10 and in FIGS. 5, 6, 7, 8 and 9.

Movable sail 34 is preferably planar and positioned fixedly on secondstrut 50 to remain perpendicular with respect to the axis of verticallyoriented outer tube 32. Movable sail 34 is preferably of generallytriangular configuration, as best illustrated in FIGS. 9 and 10, withthe sides of the triangle curving slightly inwardly. The curved edges 72of movable sail 34 converge and terminate to form small rectangularlyshaped extremities of sail 34, which are designated 76 in FIG. 9.

Movable sail 34 is positioned within generally vertically oriented outertube 32 so that rectangular extremities 76 are closely adjacent to butdo not contact the inner surface of vertically oriented outer tube 32,so long as sail 34 moves vertically up and down within verticallyoriented external tube 32. The rectangular shape of extremities 76 withtheir outwardly facing planar surface assures minimal friction andconsequent minimal resistance to movement of movable sail 34 in theevent one of rectangular extremities 76 contacts the interior surface ofvertically oriented tube 32, should sail 34 for some reason movelaterally or otherwise and become skew to the vertical axis of tube 32.

Movable internal tubular segment 42 is telescopically movable, unitarilywith sail 34, relative to and along fixed internal tubular segment 44. Alower limit of movement of movable tubular segment 42 is illustrated inFIG. 7, where the first strut portion 48 of movable tubular segment 42(shown in FIG. 10) rests on the upper circular edge of fixed internaltubular segment 44. This is the condition when no air is flowing ordrawn through the air flow limiter and gravity causes sail 34 togetherwith movable internal tubular segment 42 to drop, with first strut 48coming to rest on the upper circular edge of fixed tubular segment 44.

When air is flowing through air flow limiter 30, as illustratedgenerally in FIG. 6, the moving air pushes against movable sail 34,moving it upwardly. Movable internal tubular segment 42 moves upwardlyunitarily with sail 34 due to the fixed connection of movable tubularsegment 42 and movable sail 34 made via first and second struts 48, 50,as illustrated in FIGS. 5, 6, 7, 9, and 10.

If air flow upwardly through air flow limiter 30 reaches an extremevalue, above an acceptable level of operation of the resin deliverysystem of which air flow limiter 30 is a part, the excessive force(resulting from the high volume of air flow contacting sail 34) pushessail 34 upwardly to the point that upper annular edge 78 of movableinternal tubular segment 42 contacts plate 46. In this condition, whichis illustrated in FIG. 8, no air can pass between the upper annular edge78 of movable tubular segment 42 and flow limiting horizontal plate 46,and air flow stops.

Once air flow stops through vertically oriented outer tube 32, gravitypulling downwardly on sail 34, connected movable internal tubularsegment 42, and first and second struts 48, 50, causes these parts,which may be connected together and fabricated as a single integralassembly as shown in FIG. 8, to move downwardly, thereby againpermitting air flow upwardly through air flow limiter 30 as depictedgenerally in FIG. 6. Consequently, air flow limiter 30 isself-regulating in that when air flow is too high, the force of airmoving or impinging on sail 34 pushes movable internal tubular segment42 upwardly until upper annular edge 78 of movable tubular segment 42contacts plate 46 and no air can then escape upwardly between the upperannular edge 78 of movable tubular segment 42 and plate 46. This stopsair flow through flow limiter 30 until downward movement of sail 34together with movable internal tubular segment 42 moves upper annularedge 78 of movable tubular segment 42 away from plate 46, againpermitting air to flow through the upper extremity of movable tubularsegment 42, with air passing between upper annular edge 78 of movableinternal tubular segment 42 and flow limiting horizontal plate 46, andthen escaping through upper outlet end 56 of air flow limiter 30.

With the self-regulating characteristic of air flow limiter 30, theassembly consisting of movable internal tubular segment 42, first andsecond struts 48, 50 and sail 34 may oscillate somewhat about theposition at which air flow drawn by suction is at the desired level, asthe vacuum pump drawing air through flow limiter 30 varies in cubic feetper minute of air drawn.

Desirably, ends of first strut 48, which is depicted as beinghorizontally disposed in the drawings, are mounted in movable tubularsegment 42 in movable fashion such that first strut 48 can moveslightly, rotationally, relative to movable internal segment 42. This isto provide a small amount of “play” in the event movable sail 34 andsecond strut 50, which is vertically oriented and connected to movablesail 34, become skew with respect to the vertical axis of verticallyoriented exterior tube 32. Should this occur, the movable characteristicof first strut 48, being slightly rotatable relative to movable internaltubular segment 42, effectively precludes movable internal tubularsegment 42 from binding with respect to fixed internal tubular segment44 and thereby being restricted from what would otherwise be freelytelescoping movement of movable internal tubular segment 42 relative tofixed internal tubular segment 44.

Desirably first strut 48 is rotatable relative to movable internaltubular segment 42, to provide maximum freedom of vertical motion ofmovable internal tubular segment 42 in the event movable sail 34 becomesskew to the axis of vertically oriented exterior tube 32, withconsequent frictional force restricting vertical movement of movablesail 34.

Baffle 52 preferably includes two portions, the upper portion preferablybeing defined by fixed internal tubular segment 44 and a lower portionpreferably being defined by conical portion 66 of baffle 52. A loweredge of baffle 52 is circular and is designated 84 in the drawings.Circular edge 84 fits closely against the annular interior wall ofvertically oriented exterior tube 32 so that all air passing upwardlythrough air flow limiter 30, namely through vertically oriented exteriortube 32, is constrained to flow through the interior of baffle 52. Thetight fitting of the circular lower edge of baffle 52 against theinterior wall of vertically oriented exterior tube 32 forces all airentering flow limiter 30 from the bottom to flow through the interior ofbaffle 52, flowing upwardly through lower conical portion 66 of baffle52.

The air then flows further upwardly through the interior of fixedinternal tubular segment 44. Thereafter, if movable internal tubularsegment 42 is spaced away from flow limiting horizontal plate 46, airflows along the surface of movable internal tubular segment 42, passingthe upper annular edge 78 of movable internal tubular segment 42; airthen flows around the space between edge 82 of flow limiting horizontalplate 46 and the interior annular wall of vertically oriented exteriortube 32. The air then flows out of air flow limiter 30 via open outletend 56 formed in end cap 60.

In an alternate embodiment of the air flow limiter portion of theinvention, baffle 52 may be constructed from two pieces that fit closelytogether, with the two pieces being in facing contact in the area wherethey define fixed internal tubular segment 44, but diverging one fromanother in the area where they define conical portion 66 of baffle 52.As illustrated in FIG. 12, the two portions of baffle 52 are designated“66A” and “66B” where they diverge, with baffle portion 66A serving tochannel air flow upwardly through vertically oriented exterior tube 32into fixed internal tubular segment portion 44 of baffle 52. The spacebetween the lower parts of baffle portions 66A and 66B is filled with afiller material 86 to provide additional assurance that all air enteringvertically oriented exterior tube 32 from the bottom flows through fixedinternal tubular segment 44 and on through movable internal tubularsegment 42, and does not pass around the edge of baffle 52, namelybetween baffle 52 and the interior surface of vertically orientedexterior tube 32. Filler material 86 provides additional structuralrigidity for flow limiter 30.

In another alternative environment of the air flow limiter aspect of theinvention, baffle 52 is one piece, preferably molded plastic, asillustrated in FIG. 11, where baffle 52 is designated 52B to distinguishit from the baffle construction illustrated in FIG. 12 and the baffleconstruction illustrated in the other drawing figures. In the baffleconstruction illustrated in FIG. 11, the one piece construction meansthat there is no need or space for any filler material. The baffleconstruction illustrated in FIGS. 3 through 10 is preferred.

The assembly illustrated in FIG. 10 comprising the moveable internaltubular segment 42, first strut 48, second strut 50 and moveable sail 34may preferably be constructed as a single piece or several pieces asrequired. The assembly of moveable internal segment 42, first and secondstruts, 48, 50 and moveable sail 34 is referred to as a “sail assembly.”It is not required that first and second struts 48, 50 be separatepieces; they may preferably be fabricated as a single piece.Additionally, second strut 50, which has been illustrated as a machinescrew in FIGS. 9 and 10, need not be a machine screw. Any suitablestructure can be used for second strut 50 and it is particularlydesirable to fabricate first and second struts 48 and 50 from a singlepiece of plastic or metal, by molding, by machining or by welding, or byotherwise fastening two pieces together. Similarly with the hex nut,which is unnumbered in FIG. 10 and illustrated there, any other suitablemeans for attachment of the second strut or a vertical portion of astrut assembly to moveable sail 34 may be used.

Air flow limiter 30 preferably contains no springs. Air flow limiter 30preferably contains no sensors to provide feedback to a control device;no sensors are needed since because flow limiter 30 is self-regulating.Air flow limiter 30 preferably includes a tubular valve, closing againsta flat surface, where the tubular valve is defined by movable internaltubular segment 42 closing against flow limiting horizontal plate 46.Movable internal tubular segment 42 is in the form of an open-endedcylinder and is connected to a plate in the form of movable sail 34 tomove movable tubular segment 42 against flow limiting horizontal plate46. Air flow limiter 30 uses gravity alone to open the valve defined bythe assembly of movable internal tubular segment 42 and movable sail 34and the connecting structure therebetween.

In the air flow limiter illustrated in FIGS. 3 through 12, the movableinternal tubular segment 42 is preferably made with a very thin wall,preferably from metal tubing, where the wall is preferably less than1/32 inch in thickness.

Air flow limiter 30 functions equally well with a vacuum pump drawingair through air flow limiter 30 from bottom to top by application ofvacuum to outlet end 56 as depicted generally in FIGS. 1 and 2, or byair being supplied under positive pressure at inlet end 54 for passageupwardly through air flow limiter 30.

In the claims appended hereto, the term “comprising” is to be understoodas meaning “including, but not limited to” while the phrase “consistingof” should be understood to mean “having only and no more”.

The following is claimed:
 1. Apparatus for conveying granular plasticresin from a supply to receivers that retain and dispense the resin whenneeded by a process machine, comprising: a. a vacuum pump; b. an airflow limiter connected to a suction head of the vacuum pump; c. a firstconduit connecting the receivers to the air flow limiter; and d. asecond conduit connecting the supply to the receivers; whereby suctioncreated by operation of the vacuum pump draws granular plastic resinfrom the supply into the receivers through the second conduit and drawsair from the second conduit through the receivers, the first conduit andthe air flow limiter.
 2. Apparatus of claim 1 wherein the air flowlimiter further comprises: a. a vertically oriented tube; b. a pair ofopen-ended telescoping tubular internal segments within the tube, anouter tubular segment being fixed and the other being slide ably movablealong the fixed segment in the axial direction; c. a plate extendingpartially across the interior of the vertically oriented tube,positioned for contacting the movable one of the telescoping tubularsegments and limiting travel of the moveable telescoping tubularsegment, the plate covering an open upper end of the movable telescopingtubular segment upon contact therewith; d. a sail positioned in thevertically oriented tube below the telescoping segments; e. a strutconnecting the sail and the moveable telescoping tubular segment; f. thebaffle positioned to direct upward air flow within the tube into thetelescoping tubular segments; the movable telescoping tubular segmentmoving vertically within the tube unitarily with the sail responsive toair flow upwardly through the tube against the sail.
 3. The air flowlimiter of claim 2 wherein the tubular segments are cylindrical.
 4. Theair flow limiter of clam 2 wherein the surface of the plate contacted bythe movable tubular segment is planar.
 5. The air flow limiter of claim4 wherein the portion of the moveable tubular segment contacting theplate surface is annular.
 6. The air flow limiter of clam 2 wherein asurface of the plate contacted by the movable tubular segment is flat,the tubular segments are cylindrical, and a circular edge of the tubularsegment contacting the plate surface is annular and normal to the axisof the tubular segment.
 7. Apparatus for conveying granular plasticresin from a supply to receivers that retain and dispense the resin whenneeded by a process machine, comprising: a. a vacuum pump; b. air flowlimiters connected to outlets of the receivers; c. a first conduitconnecting the air flow limiters to a suction head of the vacuum pump;and d. a second conduit connecting the supply to the receivers; wherebysuction created by operation of the vacuum pump draws granular plasticresin from the supply into the receivers through the second conduit anddraws air from the second conduit through the receivers, the air flowlimiters and the first conduit.
 8. The apparatus of claim 7 wherein atleast one of the air flow limiters consists of: a. a tube; b. a tubularsegment within the tube being movable in the axial direction; c. a plateextending at least partially across the interior of the tube, forcontacting the movable tubular segment and defining a limit of travel ofthe movable tubular segment; d. a sail connected to the moveable tubularsegment and being movable therewith within the tube; e. a baffle,connected to and within the tube, defining a second limit of travel ofthe movable tubular segment, the moveable tubular segment being insliding telescoping engagement with a tubular portion of the baffle, thebaffle directing air flow within the tube into the tubular segment; themovable tubular segment being movable unitarily with the sail inresponse to upward air flow through the tube contacting the sail. 9.Apparatus of claim 1 wherein the air flow limiter further comprises: a.a tube; and b. a valve within and connected to the tube; and a bafflelocated within and connected to the tube, positioned to direct air flowwithin the tube against the valve.
 10. Apparatus of claim 9 wherein thevalve comprises a pair of telescoping tubular segments.
 11. Apparatus ofclaim 10 wherein the outer one of the telescoping tubular segments isfixed by and the inner one of the telescoping tubular segments isslidably moveable along the fixed segment in the axial direction withthe tube.
 12. Apparatus of claim 11 wherein the valve further comprisesa plate extending partially across the interior of the verticallyoriented tube, being connected to the tube and positioned for contactinga moveable one of the telescoping tubular segments.
 13. Apparatus ofclaim 12 wherein the valve further comprises a sail within thevertically oriented tube, connected to the moveable one of thetelescoping tubular segments.
 14. Apparatus of claim 7 wherein the airflow limiter further comprises: a. a tube; and b. a valve within andconnected to the tube; and a baffle located within and connected to thetube, positioned to direct air flow within the tube against the valve.15. Apparatus of claim 14 wherein the valve comprises a pair oftelescoping tubular segments.
 16. Apparatus of claim 15 wherein theouter one of the telescoping tubular segments is fixed and the inner oneof the telescoping tubular segments is slidably moveable along the fixedsegment in the axial direction with the tube.
 17. Apparatus of claim 16wherein the valve further comprises a plate extending partially acrossthe interior of the vertically oriented tube, being connected to thetale and positioned for contacting a moveable one of the telescopingtubular segments.
 18. Apparatus of claim 17 wherein the valve furthercomprises a sail within the vertically oriented tube, connected to themoveable one of the telescoping tubular segments.
 19. A method forconveying granular resin plastic material from a supply to receivers,comprising: a. providing a vacuum pump; b. connecting an air flowlimiter to a suction head of the vacuum pump; c. connecting thereceivers to the air flow limiter; d. connecting a supply of granularplastic resin material to the receivers; and e. actuating the vacuumpump.
 20. A method for conveying granular plastic resin material from asupply to receivers comprising: a. providing a vacuum pump; b. providinga vacuum drawing conduit connected to a suction head of the vacuum pump;c. providing an air flow limiter between each receiver and the vacuumdrawing conduit; d. providing a conveying conduit between the supply andthe receivers; and e. actuating the vacuum pump.